1. Field of the Invention
This invention relates to a device used to dynamically separate at least two zones in which there are different environments, to enable objects or products to be transferred from one zone to the other at high speed without breaking the confinement.
The process according to the invention may be used in many industrial sectors.
Thus, this process is applicable to all industries (food processing, medical, biotechnologies, high technologies, nuclear, chemical, etc.) in which different environments have to be maintained in zones communicating with each other to enable frequent passage of objects or products. The term "environment" refers particularly to aeraulic conditions, gaseous and particular concentrations, temperature, relative humidity, etc.
2. Discussion of the Background
At the present time, there are two types of solutions for dynamically separating two zones communicating with each other, for example in order to allow objects to be brought in and out; these two types are protection by ventilation and protection by air curtain.
Protection by ventilation consists of artificially creating a pressure difference between the two zones so that the pressure in a zone to be protected is greater than the pressure inside a contaminating zone. Thus, if the zone to be protected contains a product that could be contaminated by ambient air, a laminar flow is injected into the zone to be protected that blows outwards through the access opening to this separation zone. In the opposite case in which personnel and the environment outside a contaminated space need to be protected, dynamic confinement is achieved by using extraction ventilation in this contaminated space. In each case, an empirical rule imposes a minimum ventilated air speed of 0.5 m/s in the plane of the opening through which the two zones communicate in order to prevent contamination from being transferred into the zone to be protected.
However, the efficiency of this ventilation protection technique is not perfect, particularly in a so-called "infractions" situation, in other words when objects are transferred between the two zones. Furthnermore, this type of protection makes it necessary to process and control the entire zone to be protected ron the contaminating external atmosphere or the entire contaminated zone. When the zone to be processed and controlled is large, this introduces a particularly high investment and operating cost. Finally, this technique of protection by ventilation only provides protection in one direction, in other words it is onlv useful when contamination transfers are only possible in one direction.
The air curtain protection technique consists of simultaneously injecting one or several adjacent clean air jets in the same direction into the separation zone between the two zones, which form an immaterial door between the zone to be protected and the contaminating zone.
Note that according to the theory of turbulent plane jets, a plane air jet is composed of two separate zones; a transition zone (or core zone) and a development zone.
The transition zone corresponds to the central part of the jet adjacent to the nozzle in which clean air is injected. Within this zone in which there is no mix between the injected air and the air on each side of the jet, the speed vector is constant. Considering a cross-section through a plane perpendicular to the plane of the separation zone, the width of the transition zone gradually decreases as the distance from the nozzle increases. This is why this transition zone is called a "tongue" throughout the rest of the text.
The-development zone of the jet is the part of this jet located outside the transition zone. In this jet development zone, outside air is entrained by the jet low. This results in variations in the speed vector and mixing of air. Air entrainment on both surfaces of the jet within this development zone is called "induction". Thus an air jet induces an air flow on each of its surfaces which depends particularly on the injection flow of the jet considered.
Documents FR-A-2 530 163 and FR-A-2 652 520 propose an air curtain to separate a polluted zone from a clean zone. in both cases, the air curtain consists of twio adjacent clean air jets blowing in the same direction. Nllore precisely, dynamic separation is provided by a first relatively slow jet (called the "slow jet"), for which the tongue entirely covers the opening. The second jet (called the "fast jet") is faster than the slow jet, and is installed between the slow jet and the zone. Its function is to stabilize the slow jet by a suction effect which brings this slow jet into contact with the fast jet.
In these documents, it is specified that the tongue of the slow jet is sufficiently long to cover any opening when the width of the slow jet injection nozzle is equal to at least 1/6.sup.th of the height of the opening to be protected.
Document FR-A-2 652 520 also proposes to simultaneously inject clean ventilation air at a temperature adapted to the requirements, inside the clean zone to be protected. Note that this clean ventilation air must be injected at a rate approximately equal to the rate induced by the surface of the fast jet which is in contact with clean ventilation air.
Furthermore, document FR-A-2 659 782 proposes to add a third relatively slow clean air jet to the two clean air jets used in documents FR-A-2 530 163 and FR-A-2 652 520 so that the fast jet is located between two adjacent slow jets in the same direction. The flow of clean ventilation air injected inside the zone to be protected is then considerably reduced due to the fact that induction in this zone is produced by the development zone of one of the slow jets, rather than by the development zone of the fast jet as in the case of an air curtain with two jets. Furthermore, dynamic confinement is provided in both directions, which was not the case in the previous documents.
Document WO-A-96 241011 also describes an installation in which a chamber containing a confined atmosphere, communicates with the same outside atmosphere through one or two openings, with which gas curtains are associated. Each gas curtain is formed of a slow jet sustained by a fast jet as described in documents FR-A-2 530 163 and FR-A-2 652 520. The chamber can be used for continuous processing of products due to the injection of a reagent inside it. Products pass from the outside atmosphere into the confined atmosphere in this chamber to be processed in it before being taken out again to the external atmosphere.
Despite the improvements made to the air curtain technique described in these various documents, the problem of transferring objects or products at a high rate between two zones in which there are different environments without breaking the confinement has not been satisfactorily solved by any known device, particularly if there is a risk of cross-contamination between the two zones.